Table of wafer polishing apparatus, method for polishing semiconductor wafer, and method for manufacturing semiconductor wafer

ABSTRACT

A table for a wafer polishing apparatus having superior heat-resistant, anti-thermal-shock, and anti-abrasion characteristics and capable of increasing the diameter of a semiconductor wafer while improving the quality of the wafer. The table ( 2 ) includes a plurality of superimposed bases ( 11 ) each of which is formed of silicide ceramic or carbide ceramic. The bases ( 11 ) are joined together by an adhesive layer ( 14 ). A fluid passage ( 12 ) is formed in a joining interface between the bases ( 11 ).

The present invention relates to a table of a semiconductor waferpolishing apparatus, a method for polishing semiconductor wafers withthe polishing apparatus, and a method for manufacturing a semiconductorwafer with the polishing apparatus.

BACKGROUND OF THE INVENTION

These days, most electric products employ a semiconductor device thatincludes a fine conductive circuit formed on a silicone chip. Generally,the semiconductor device is fabricated using a monocrystal silicon ingotas a starting material in accordance with the following procedure.

First, the ingot is sliced into thin pieces. The pieces are thenpolished in a lapping step and a polishing step to obtain bare wafers.The bare wafers include mirror surfaces and are thus referred to asmirror wafers. Also, if the bare wafers are obtained in an epitaxialgrowth layer forming step after the lapping step and before thepolishing step, the bare wafers are particularly referred to asepitaxial wafers.

In a subsequent wafer treating step, the bare wafers are repeatedlysubjected to oxidation, etching, and impurity diffusion. Afterwards, thebare wafers are cut into an appropriate size in a dicing step. Thisfinally completes a desired semiconductor device.

In these steps, a device forming side of each semiconductor wafer needsbe polished with a certain means. As an effective polishing means,various types of wafer polishing apparatuses (including lapping machinesand polishing machines) have been proposed.

A typical wafer polishing apparatus includes a table, a pusher plate,and a cooling jacket. The table is secured to an upper portion of thecooling jacket. The table and the cooling jacket are formed of metalsuch as stainless steel. A passage is formed in the cooling jacket andcoolant water for cooling the table circulates in the passage. Thepusher plate is located above the table and has a holding side (a lowerside) to which a wafer subject to polishing is adhered by athermoplastic wax. The pusher plate rotates to press the wafer, which isheld by the pusher plate, against a polishing side (an upper side) ofthe table from above. The wafer thus contacts the polishing side, andone side of the wafer is uniformly polished. During polishing, heat isgenerated on the wafer and is transmitted to the cooling jacket throughthe table. The coolant water that circulates in the passage of thecooling jacket releases the heat from the apparatus.

The table of the wafer polishing apparatus is often heated to a hightemperature when polishing is performed. It is thus required that thetable be formed of a heat-resistant and thermal-shock-resistantmaterials. Further, frictional force constantly acts on the polishingside of the table. It is thus required that the material of the tableneed be resistant to abrasive wear. In addition, generation of thermalstress that bends the wafer must be avoided to increase the waferdiameter and improve the wafer quality. It is thus necessary to minimizetemperature differences in the table. Accordingly, the material of thetable needs to have high heat conductivity.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a table of awafer polishing apparatus that has superior heat-resistant,thermal-shock-resistant, and anti-abrasion characteristics and iscapable of increasing the diameter of a semiconductor wafer whileimproving the wafer quality.

It is another objective of the present invention to provide a method forpolishing semiconductor wafers and a method for manufacturing thesemiconductor wafers that are optimal for uniformly polishing thesemiconductor wafers to increase the wafer diameter and improve thewafer quality.

To solve the above-described problems in accordance with the objectivesof the present invention, an improved table of a wafer polishingapparatus is provided. The table has a polishing surface for polishing asemiconductor wafer held by a wafer holding plate of the wafer polishingapparatus. The table includes a plurality of superimposed bases, eachbase being formed from silicide ceramic or carbide ceramic. At least oneof the bases has a fluid passage formed in its superimpositioninterface.

In a second perspective of the present invention, the table includes aplurality of superimposed bases, each base being formed from a siliconcarbide sinter. At least one of the bases has a fluid passage formed inits superimposition interface.

A third perspective of the present invention is a table having apolishing surface for polishing a semiconductor wafer held by a waferholding plate of a wafer polishing apparatus. The table is formed of amaterial, the Young's modulus of which is 1.0 kg/cm²(×10⁶) or greater.

A fourth perspective of the present invention provides a method forperforming polishing using a table having a polishing surface forpolishing a semiconductor wafer held by a wafer holding plate of a waferpolishing apparatus. The table includes a plurality of superimposedbases, each base being formed from silicide ceramic or carbide ceramic.At least one of the bases has a fluid passage formed in itssuperimposition interface. The method includes the steps of rotating thesemiconductor wafer, and contacting the semiconductor wafer with thepolishing surface of the table while circulating coolant water in thefluid passage.

A fifth perspective of the present invention provides a method formanufacturing a semiconductor wafer. The method includes performingpolishing using a table having a polishing surface for polishing asemiconductor wafer held by a wafer holding plate of a wafer polishingapparatus. The table includes a plurality of superimposed bases, eachbase being formed from silicide ceramic or carbide ceramic. At least oneof the bases has a fluid passage formed in its superimpositioninterface. The polishing step includes the steps of rotating thesemiconductor wafer, and contacting the semiconductor wafer with thepolishing surface of the table while circulating coolant water in thefluid passage.

A sixth perspective of the present invention is a method formanufacturing a table having a polishing surface for polishing asemiconductor wafer held by a wafer holding plate of a wafer polishingapparatus. The method includes the steps of arranging a foil-likebrazing filler between a plurality of bases, each having a groove formedin its surface and each formed from a silicon carbide sinter, andheating each of the bases to braze the bases together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a wafer polishing apparatus of afirst embodiment according to the present invention;

FIG. 2 is an enlarged cross-sectional view showing a main portion of atable used in the apparatus of FIG. 1;

FIG. 3 is an enlarged view schematically showing a main portion of atable according to a first modification of the first embodiment;

FIG. 4 is an enlarged view schematically showing a main portion of atable according to a second modification of the first embodiment;

FIG. 5 is an enlarged cross-sectional view showing a main portion of atable according to a third modification of the first embodiment;

FIG. 6 is a view schematically showing an apparatus of a secondembodiment according to the present invention;

FIG. 7 is an enlarged cross-sectional view showing a main portion of atable used in the apparatus of FIG. 6;

FIG. 8 is an enlarged cross-sectional view showing a main portion of atable according to a first modification of the second embodiment;

FIG. 9 is an enlarged cross-sectional view showing a main portion of atable according to a second modification of the second embodiment;

FIG. 10 is an enlarged cross-sectional view showing a main portion of atable according to a third modification of the second embodiment;

FIG. 11 is a view schematically showing an apparatus of a thirdembodiment according to the present invention;

FIG. 12 is an enlarged cross-sectional view showing a main portion of atable used in the apparatus of FIG. 11;

FIG. 13A is an enlarged cross-sectional view showing a main portion of atable used in an apparatus of a sixth embodiment according to thepresent invention;

FIGS. 13B and 13C are further enlarged cross-sectional views eachschematically showing an adhering interface of the table;

FIG. 14 is an enlarged cross-sectional view schematically showingcrystal particles in the adhering interface of the table of the sixthembodiment;

FIG. 15 is an enlarged cross-sectional view showing a main portion of atable according to a first modification of the sixth embodiment; and

FIG. 16 is an enlarged cross-sectional view showing a main portion of atable according to a second modification of the sixth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A wafer polishing apparatus 1 of the first embodiment will now bedescribed in detail with reference to FIGS. 1 and 2. FIG. 1schematically shows the wafer polishing apparatus 1 of the firstembodiment. The wafer polishing apparatus 1 includes a disk-like table2. A polishing surface 2 a, on which a semiconductor wafer 5 ispolished, is defined on the upper side of the table 2. A polishing cloth(not shown) is applied to the polishing surface 2 a. In the firstembodiment, a cooling jacket is not employed, and the table 2 ishorizontally and directly secured to an upper end of a cylindricalrotary shaft 4. Thus, when the rotary shaft 4 is rotated, the table 2rotates integrally with the rotary shaft 4.

As shown in FIG. 1, the wafer polishing apparatus 1 includes a pluralityof wafer holding plates 6 (for the sake of brevity, only two are shownin FIG. 1). Each plate 6 is formed of, for example, glass, ceramic suchas alumina, or metal such as stainless steel. A pusher rod 7 is fixed toa middle portion of one side (a non-holding side 6 b) of each waferholding plate 6. Each pusher rod 7 is located above the table 2 and isconnected to a drive means (not shown). Each pusher rod 7 horizontallysupports the associated wafer holding plate 6. In this state, theholding sides 6 a oppose the polishing surface 2 a of the table 2.Further, each pusher rod 7 rotates integrally with the associated waferholding plate 6 and moves upward and downward in a predetermined range.In addition to the upward or downward movement of the plates 6, thetable 2 may be configured to move upward or downward. A semiconductorwafer 5 is adhered to the holding surface 6 a of each wafer holdingplate 6 by an adhesive agent such as thermoplastic wax. Thesemiconductor wafers 5 may be vacuumed or electrostatically attracted tothe corresponding holding sides 6 a. In this state, a polished surface 5a of each semiconductor wafer 5 must be faced toward the polishingsurface 2 a of the table 2.

If the apparatus 1 is used as a lapping machine, or is used forpolishing the semiconductor wafers 5 after a slicing step of a barewafer process is completed, it is preferred that the wafer holdingplates 6 be configured as follows. That is, it is preferred that eachplate 6 allow the corresponding semiconductor wafer 5 to contact thepolishing surface 2 a in a state in which a predetermined pressure isapplied to the polishing surface 2 a. This is possible since the wafer 5does not include an epitaxial growth layer, which the wafer holdingplate 6 (the pusher plate) would remove from the wafer 5 when applyingpressure. It is preferred that the wafer holding plates 6 be configuredin the same manner if the apparatus 1 is used as a polishing machine formanufacturing mirror wafers, or is used for polishing the semiconductorwafers 5 without performing an epitaxial growth step after the lappingstep is completed.

If the apparatus 1 is used as a polishing machine for manufacturingepitaxial wafers, or is used for polishing the semiconductor wafers 5that have been subjected to the epitaxial growth step after the lappingstep, it is preferred that the plates 6 be configured as follows. Thatis, it is preferred that each plate 6 have the correspondingsemiconductor wafer 5 contact the polishing surface 2 a while applyingsubstantially no pressure to the polishing surface 2 a. This is becausea silicone epitaxial growth layer easily separates compared tomonocrystal silicon. It is preferred that the wafer holding plates 6 beconfigured basically in the same manner if the apparatus 1 is used as amachine for performing chemical mechanical polishing (CMP) after variouslayer forming steps.

The structure of the table 2 will hereafter be described in detail.

As shown in FIGS. 1 and 2, the table 2 of the first embodiment is asuperimposed ceramic body that includes a plurality of (in thisembodiment, two) superimposed bases 11A, 11B. Among the two bases 11A,11B, grooves 13 having a predetermined pattern are formed in the upperside of the lower base (hereafter, the lower base 11B). The bases 11A,11B are joined together by a brazing filler layer 14, or a non-organicadhering material layer, thus forming an integral body. Accordingly, acoolant water passage 12, or a fluid passage, is formed in the joininginterface between the bases 11A, 11B. That is, the grooves 13 form partof the coolant water passage 12. A plurality of through holes 15 areformed in the middle of the lower base 11B. The through holes 15 connecta passage 4 a formed in the rotary shaft 4 to the coolant water passage12.

Each base 11A, 11B is formed from a ceramic material. It is preferredthat the material be ceramic silicide or ceramic carbide. Particularly,in the first embodiment, the ceramic material is a dense body that isformed from a silicon carbide sinter (SiC sinter), the starting materialof which is silicon carbide powder. The dense body has strongly bondedcrystal particles and an extremely small number of pores. The dense bodyis thus suitable as the material of the table. Further, compared toother ceramic sinters, the silicon carbide sinter, the starting materialof which is silicon carbide powder, includes particularly superior heatconductivity, heat-resistant performance, anti-thermal-shockperformance, and anti-abrasion performance characteristics. In the firstembodiment, the two bases 11A, 11B are formed from the same material.

The silicon carbide powder includes a type silicon carbide powder, βtype silicon carbide powder, and amorphous silicon carbide powder. Inthis case, one type of powder may be solely employed. Alternatively, twoor more types of powders may be combined (α type+β type, atype+amorphous type, β type+amorphous type, or a type+β type+amorphoustype). A sintered formed from β type silicon carbide powder includes alarge number of large plate crystals compared to sinters of other typesof silicon carbide powders. Thus, the sinter formed from β type siliconcarbide powder includes a relatively small number of grain boundaries inthe crystal particles of the sinter and has particularly superior heatconductivity.

The density of the bases 11A, 11B is preferred to be 2.7 g/cm³ orgreater, is more preferred to be 3.0 g/cm³ or greater, and is especiallypreferred to be 3.1 g/cm³ or greater. If the density is excessively low,the bonding among the crystal particles of the sintered body is weakenedand the number of the pores increases. This results in the bases 11A,11B having unsatisfactory anti-corrosion and anti-abrasioncharacteristics.

It is preferred that the heat conductivity of each base 11A, 11B be 30W/m·K or greater and more preferred that the heat conductivity be 80W/m·K to 200 W/m·K. If the heat conductivity is excessively low, thereis a tendency of temperature differences being produced in the sinter,thus hampering the increasing of the diameter of the semiconductorwafers 5 and improvement of the wafer quality. On the other hand,although the heat conductivity is preferred to be higher, it becomesdifficult to procure materials inexpensively and stably when the heatconductivity exceeds 200 W/m·K.

The groove 13, which forms part of the coolant water passage 12, is agrounded groove, or is formed by grinding the upper side of the lowerbase 11B with a grinder. The groove 13 does not necessarily have to beground but may be formed through, for example, blasting such as sandblasting. As schematically shown in FIG. 2, the groove 13, which isformed through these processes, has a relatively round cross-sectionalshape. It is preferred that the depth of the groove 13 be approximately3–10 millimeters and that the width of the groove 13 be approximately5–20 millimeters.

A procedure for fabricating the table 2 will hereafter be brieflydescribed.

First, a small amount of sintering aiding agent is added to siliconcarbide powder and uniformly mixed. Boron, boron compound, aluminum,aluminum compound, or carbon is selected as the sintering aiding agent.The addition of the small amount of the sintering aiding agent increasesthe crystal growth speed of silicon carbide such that a resulting sinteris dense and has high heat conductivity.

Next, the mixture is molded into disk-like molded products. The bodiesare then calcinated at 1800 to 2400 degrees Celsius to obtain the twobases 11A, 11B, each of which is a silicon carbide sinter. If thecalcinating temperature is too low, not only does it become difficult toincrease the crystal particle diameter but also a large number of poresare formed in the sintered body. In contract, if the calcinatingtemperature is too high, silicon carbide starts to decompose and lowersthe strength of the sintered body.

Subsequently, one side of the lower base 11B is substantially entirelyground with a grinder to form the grooves 13, which have a predeterminedwidth and a predetermined depth. Further, after applying the brazingfiller to on one side of the upper base 11A, the two bases 11A, 11B aresuperimposed to arrange the brazing filler layer 14 and the groove 13 inthe interface between the bases 11A, 11B. In this state, the bases 11A,11B are heated to the melting temperature of the brazing filler, thusbrazing the bases 11A, 11B together. Finally, the upper side of theupper base 11A is polished to form the polishing surface 2 a. Thesurface polishing step may be performed before the adhesion step or thegroove formation step. The table 2 of the first embodiment is thusformed in the above-described procedure.

The following are referential examples of the first embodiment.

Referential Example 1-1

In referential example 1-1, “beta random (trade name)”, product ofIBIDEN KABUSHIKI KAISHA, was used as silicon carbide powder thatcontained 94.6 weight percent of β type crystals. The average crystalparticle diameter of this powder was 1.3 micrometers. The powdercontained 1.5 weight percent of boron and 3.6 weight percent of freecarbon.

First, 5 weight parts of polyvinyl alcohol and 300 weight parts of waterwere added to 100 weight parts of the silicon carbide powder. Themixture was then stirred in a ball mill for five hours to obtain auniform mixture. The mixture was dried for a predetermined time toremove a certain amount of moisture from the mixture. An appropriateamount of the dry mixture was then sampled and granulated. Next, thegranules of the dry mixture were subjected to molding with metal pressdies at a pressure of 50 kg/cm². The density of the resulting moldedbody was 1.2 g/cm³.

Subsequently, the molded body was placed in a graphite crucible sealedfrom ambient air. The body was then calcinated using a Tammann typecalcinating furnace. The calcination was performed in an argon gasatmosphere of one atmospheric pressure. During the calcination, theheating was increased at a rate of 10 degrees Celsius per minute untilreaching a maximum temperature of 2300 degrees Celsius. The maximumtemperature was maintained for two hours. The observation of theresulting bases 11A, 11B indicated an extremely dense, three-dimensionalnetwork structure in which plate crystals were entangled in multipledirections. Further, the density of each base 11A, 11B was 3.1 g/cm³.The heat conductivity of each base 11A, 11B was 150 W/m·K. Each base11A, 11B contained 0.4 weight percent of boron and 1.8 weight percent offree carbon.

Afterwards, the grooves 13 were ground to a depth of 5 millimeters and awidth of 10 millimeters. The two bases 11A, 11B were then integrallybrazed to each other. The thickness of the brazing filler layer 14 wasabout 20 micrometers. Further, the upper side of the upper base 11A waspolished to form the table 2 that had the polishing surface 2 a.

The resulting table 2 of referential example 1-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers5 of different dimensions were then polished with the apparatuses 1,while the coolant water W was constantly circulating. As a result,regardless of the type of the apparatus 1, thermal deformations were notfound in the table 2. Further, cracks were not found in the brazingfiller layer 14, and a high bonding strength was maintained in thejoining interface between the bases 11A, 11B. Also, a breakage test wasconducted on the table 2 using a conventional method that complies withJIS R 1624 to measure the flexural strength of the interface. The valuewas approximately 15 kgf/mm². Further, there was no leakage of thecoolant water W from the joining interface.

The observation of the semiconductor wafers 5 polished by theapparatuses 1 indicated that the wafers 5 were not damaged, regardlessof the dimensions of the wafers 5. Further, there was no significantbending in the wafers 5. In other words, it was apparent that thesemiconductor wafers 5 having extremely high accuracy and extremely highquality would be obtained by the table 2 of referential example 1-1.

Referential Example 1-2

In referential example 1-2, a type silicon carbide powder (morespecifically, “OY15 (trade name)”, product of YAKUSHIMA DENKO KABUSHIKIKAISHA) was employed in lieu of the β type. The density of eachresulting base 11A, 11B was 3.1 g/cm³. The heat conductivity of eachbase 11A, 11B was 125 W/m·K. Each base 11A, 11B contained 0.4 weightpercent of boron and 1.8 weight percent of free carbon. The heatconductivity of the bases 11A, 11B in referential example 1-1, in whichthe β type powder was the starting material, was approximately 20percent higher than that of referential example 1-2.

After the table 2 was obtained through the same procedure as referentialexample 1-1, the table 2 was installed in the various types ofapparatuses 1 to polish the semiconductor wafers 5 of differentdimensions. Accordingly, substantially the same advantageous results asthose of referential example 1-1 were obtained.

Conclusion

The first embodiment has the following advantages.

(1) In the table 2 of the wafer polishing apparatus 1, the coolant waterW circulates in the passage 12 located in the interface between thebases 11A, 11B. Thus, when the polishing of the semiconductor wafers 5generates heat, the heat is released efficiently and directly from thetable 2. This ensures the diffusion of the heat. Accordingly, comparedto the prior art in which the table 2 is mounted on the cooling jacketand indirectly cooled, the temperature difference of the table 2 isfurther decreased. As a result, the apparatus 1 prevents the wafers 5from being adversely affected by the heat and enables the diameter ofthe wafers 5 to be increased. Further, the wafers 5 are polished withhigh accuracy. This improves the quality of the wafers 5.

(2) The table 2 forms a superimposed structure that includes the twobases 11A, 11B. Thus, after forming the structure that functions as thepassage 12 (that is, the groove 13) in one surface of one of the bases11, the bases 11A, 11B are joined together. This makes it relativelyeasy to form the passage 12 in the interface between the bases 11A, 11B.Thus, the table 2 is advantageous in that the table 2 is formedrelatively easily. Further, this structure does not need to locate apipe in the joining interface between the bases 11A, 11B. This preventsthe structure of the table 2 from becoming complicated and increases incost.

(3) The two bases 11A, 11B of the table 2 are both dense, sinteredsilicon carbide bodies, the starring material of which is siliconcarbide powder. The dense bodies are preferred in that crystal particlesare strongly bonded together and the number of the pores is extremelysmall. Further, the sintered silicon carbide body, the starting materialof which is silicon carbide powder, includes superior heat conductivity,heat-resistant, anti-thermal-shock, and anti-abrasion characteristicscompared to other sintered ceramic bodies. Thus, the table 2 of thebases 11A, 11B enables the diameter of each semiconductor wafer 5 to beincreased and improves the quality of the wafer 5.

(4) The bases 11A, 11B are securely joined together by the brazingfiller layer 14, or the joining material layer. Thus, as compared to thecase in which the bases 11A, 11B are joined together without the joiningmaterial layer, an increased joining strength is ensured in theinterface between the bases 11A, 11B. Accordingly, leakage from thejoining interface does not occur when the coolant water W circulates inthe passage 12.

If the joining material layer is the brazing filler layer 14 that has arelatively high heat conductivity, heat resistance is reduced in thejoining material layer, thus making it difficult to hamper heat transferbetween the bases 11A, 11B. This increases heat radiation from the table2 and further minimizes the temperature differences in the table 2. Thisalso contributes to the increasing of the diameter of each semiconductorwafer 5 and the improvement of the quality of the wafer 5.

(5) If the wafer polishing apparatus 1 includes the table 2, the coolingjacket becomes unnecessary, thus simplifying the entire structure of theapparatus 1.

The first embodiment may be modified as follows.

The joining material layer that joins the bases 11A, 11B together do notnecessarily have to be formed of a non-organic joining material such asa brazing filler but may be formed of an organic joining material thatcontains resin (i.e., an adhesive agent).

The bases 11A, 11B do not necessarily have to be joined together by thejoining material layer. For example, in the table 2 of the modificationshown in FIG. 3, the joining material layer is eliminated. Instead, thebases 11A, 11B of the table 2 are fastened together by a bolt 23 and anut 24, thus forming an integral body. Further, a seal member 22, suchas a packing, is located in the interface between the bases 11A, 11B toensure sufficient seal performance. It is especially preferred that theseal member 22 be formed of a material having high heat conductivity. Ifthe fastening force of the bolt 23 and the nut 24 is strong enough, theseal member 22 may be eliminated like the further modification shown inFIG. 4.

Instead of the double layered structure, the table 2 may be a triplelayered structure like the modification shown in FIG. 5. Further, thetable 3 may include four or more layers.

As silicide ceramic other than silicon carbide, for example, siliconnitride (Si₃N₄) or sialon may be selected. It is preferred that theselected silicide ceramic be a dense body with a density of 2.7 g/cm³ orgreater.

As carbide ceramic other than silicon carbide, for example, boroncarbide (B₄C) may be selected. It is preferred that the selected carbideceramic be a dense body with a density of 2.7 g/cm³ or greater.

In the table 2 of the first embodiment, liquid other than water maycirculate through the passage 12. Also, gas may circulate through thepassage 12.

Second Embodiment

A wafer polishing apparatus 1 of a second embodiment will now bedescribed in detail with reference to FIGS. 6 and 7.

As shown in FIGS. 6 and 7, like the first embodiment, the table 2 of thesecond embodiment is a layered ceramic structure that includes the twosuperimposed bases 11A, 11B. The grooves 13, which have a predeterminedpattern, are formed in substantially the entire upper side of the lowerbase 11B. The bases 11A, 11B are integrally joined together by an epoxyresin type adhesive agent layer 14, or an organic joining materiallayer.

A pipe made from a material having high heat conductivity is formed inthe interior of the table 2. The coolant water W, or fluid, circulatesin the pipe. More specifically, in the second embodiment, a copper pipe16 is located in the joining interface between the bases 11A, 11B.Copper is selected as the material of the pipe since it is inexpensive,and easily machined in addition to having a high heat conductivity.

The copper pipe 16 has a circular cross-section. The diameter of thepipe 16 is approximately 5–10 millimeters. The pipe 16 is curved to forma spiral shape as a whole. The adjacent sections of the pipe 16 at itscurved portions are spaced from each other at an interval ofapproximately 5–20 millimeters. The curved pipe 16 is held in the groove13, which is formed in the upper side of the lower base 11B. In thisstate, the bases 11A, 11B are joined together. The copper pipe 16occupies substantially the entire joining interface. Both ends of thepipe 16 are bent downward at a right angle and are received in thecorresponding through holes 15. The ends of the pipe 16 are thusconnected to the corresponding passages 4 a, which extend through therotary shaft 4.

It is preferred that the adhesive agent layer 14 for joining the bases11A, 11B be formed from an epoxy resin type adhesive agent. This isbecause this type of adhesive agent resists heat and has superioradhering strength. In this case, it is preferred that the thickness ofthe adhesive agent layer 14 be approximately 10 to 30 micrometers.Further, it is preferred for the adhesive agent to have a thermosettingproperty.

A procedure for fabricating the table 2 of the second embodiment willhereafter be described briefly.

First, like the first embodiment, the two bases 11A, 11B, each of whichis formed by a silicon carbide sinter, are formed through molding andcalcinating, using silicon carbide as a starting material.

Subsequently, one side of the lower base 11B is ground with a grinder toform the grooves 13 with a predetermined width and a predetermined depthin substantially the entire surface. Further, the adhesive agent isapplied on one side of the upper base 11A, and the pipe 16 is arrangedin the grooves 13. The two bases 11A, 11B are then superimposed. In thisstate, the bases 11A, 11B are heated to the hardening temperature of theresin, thus joining the bases 11A, 11B together. Finally, the upper sideof the upper base 11 is polished to form the polishing surface 2 a andcomplete the table 2.

The following are referential examples of the second embodiment.

Referential Example 2-1

In referential example 2-1, like referential example 1-1, the bases 11A,11B, which were formed of sintered silicon carbide bodies, were molded,using silicon carbide powder that contained β type crystals as astarting material, and calcinated. Further, the copper pipe 16, thediameter of which was 6 millimeters, was prepared and bent into apredetermined shape.

Next, the groove 13, the depth of which was 10 millimeters and the widthof which was 10 millimeters, was ground in the upper side of the lowerbase 11B. The curved portion of the copper pipe 16 was then fitted inthe groove 13. In this state, the bases 11A, 11B were integrally adheredtogether with an epoxy resin type adhesive agent. The thickness of theadhesive agent layer 14 was approximately 20 micrometers. Further, theupper side of the upper base 11A was polished to complete the table 2.

The resulting table 2 of referential example 2-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers5 of different dimensions were then polished with the apparatuses 1 withthe coolant water W constantly circulating through the copper pipe 16.Thermal deformations were not found in the table 2. Further, theadhesive agent layer 14 did not crack, and the joining strength of thejoining interface between the bases 11A, 11B was high. Also, a breakagetest was conducted on the table 2 using a conventional method complyingwith JIS R 1624 to measure the flexural strength of the interface. Thevalue was approximately 4 kgf/mm². Further, no leaks of coolant water Wfrom the joining interface were noted.

Observation of the semiconductor wafers 5 polished by the apparatuses 1indicated that the wafers 5 were not damaged regardless of thedimensions of the wafers 5. Further, no significant bending was found inthe wafers 5. In other words, it was apparent that the table 51 ofreferential example 2-1 manufactured the semiconductor wafers 5 withextremely high accuracy and extremely high quality.

Referential Example 2-2

In referential example 2-2, like referential example 1-2, the bases 11A,11B, which were formed of sintered silicon carbide bodies, were molded,using silicon carbide powder that contained α type crystals as astarting material, and calcinated. Afterwards, the table 2 was completedby the same procedure as that of referential example 2-1. The table 2was then installed in the aforementioned various types of apparatuses 1to polish the semiconductor wafers 5 that had different dimensions.Accordingly, substantially the same superior results as those ofreferential example 2-1 were obtained.

Conclusion

The second embodiment has the following advantages.

(1) In the table 2 of the second embodiment, the coolant water Wcirculates through the copper pipe 16, which is formed from a materialhaving highly heat conductivity and which is located in the joininginterface between the ceramic bases 11A, 11B. Thus, when the polishingof semiconductor wafers 5 generates heat, the heat is releasedefficiently and directly from the table 2. This radiates the heat.Accordingly, compared to the prior art in which the table 2 is mountedon the cooling jacket to indirectly cool the table 2, the temperaturedifferences in the table 2 is further decreased. As a result, theapparatus 1 prevents the wafers 5 from being adversely affected by theheat and enables the diameter of the wafers 5 to be increased. Further,the wafers 5 can be polished with high accuracy, thus improving thequality of the wafers 5.

(2) In the table 2 of the second embodiment, the coolant water Wcirculates in the pipe 16. Thus, the table 2 is advantageous in that thebases 11 are not exposed directly to the coolant water W. Further, thisstructure prevents the coolant water W from leaking from the joininginterface.

(3) The table 2 employs a layered structure that includes the two bases11A, 11B. Thus, after forming the grooves 13 in the upper surface of thelower base 11B and arranging the pipe 16 in the grooves 13, the bases11A, 11B are joined together with the adhesive agent. This makes itrelatively easy to form the coolant water passage 12 in the interfacebetween the bases 11A, 11B. As a result, the table 51 is advantageous inthat the table is easily fabricated.

(4) The two bases 11A, 11B of the table 2 are both dense bodies formedfrom silicon carbide sinters, the starting materials of which aresilicon carbide powder. The dense bodies are preferred in that crystalparticles are strongly bonded together and the number of the pores isextremely small. Further, the sintered silicon carbide body, thestarting material of which is silicon carbide powder, includes superiorheat conductivity, heat-resistant, anti-thermal-shock, and anti-abrasioncharacteristics compared to other sintered ceramic bodies. Thus, byusing the table 2 formed by the bases 11A, 11B to perform polishing, thediameter of each semiconductor wafer 5 may be increased while improvingthe quality of the wafer 5.

(5) In the table 2, the copper pipe 16 is held in the groove 13. Thus,as shown in FIG. 7, the bases 11A, 11B are adhered together locatedclose to each other. This reduces the thickness of the adhesive agentlayer 14, thus preventing the adhesive agent layer 14 from cracking. Thejoining strength of the adhesive agent layer 14 thus increases.Accordingly, the table 2 is not easily damaged by heat.

(6) In the table 2, the grooves 13 have a round cross-section, andgrooves 13 accommodate the pipe 16, the cross-section of which is round.This reduces the space formed between the inner wall of the groove 13and the outer side of the pipe 16 when the pipe 16 is accommodated inthe groove 13. Thus, the amount of the adhesive agent layer 14 fillingthe space between the inner wall of the groove 13 and the outer side ofthe pipe 16 is small. This reduces heat resistance of the adhesive agentlayer 14 accordingly. As a result, the heat releasing effect isimproved, and the temperature differences in the table 2 are furtherdecreased.

(7) In the second embodiment, the pipe material is copper, which isinexpensive and easy to machine. This decreases the cost of the table 2.Further, copper has high heat conductivity. Thus, the copper pipe 16improves the heat radiating effect and suppresses the temperaturedifferences in the table 2.

(8) If the table 2 of the second embodiment is installed in the waferpolishing apparatus 1, the cooling jacket is not required. Thissimplifies the apparatus structure as a whole.

The second embodiment may be modified as follows.

In a modification of the table 2, as shown in FIG. 8, powder formed froma substance having a high heat conductivity is mixed in the adhesiveagent layer 14 at least in the space around the pipe 16 as a filler. Itis preferred that a copper powder 17 that has an average particlediameter of approximately 50 to 200 micrometers is selected as thepowder. It is also preferred that the copper powder 17 be concentratedonly around the pipe 16 in the adhesive agent layer 14, or that theamount of the copper powder 17 in the joining interface between thebases 11A, 11B be minimal. This increase heat conductivity of thejoining interface between the bases 11A, 11B and increases the joiningstrength of the interface.

Other than the copper powder 17, the powder may be at least one type ofmetal powder selected from, for example, gold, silver, and aluminum.Further, the powder may be a ceramic powder such as alumina, aluminumnitride, and silicon carbide.

The table 2, modified as described above, is fabricated by a procedurein which the grooves are first formed in the upper side of the lowerbase 11B, the copper powder 17 is then filled in the groove 13, and, inthis state, adhesive agent is applied to join the base 11A, 11Btogether.

Instead of the table 2 that has the double layered structure, the table2 may be formed as a triple layered structure, as shown in amodification of FIG. 9. Further, the table 2 may be a structure that hasfour or more layers.

In a modification of the table 2, as shown in FIG. 10, the bases 11A,11B may be joined together with the copper pipe 16 placed along a flatsurface, without forming the groove 13 for receiving the pipe in theupper side of the lower base 11B.

The material of the pipe 16 is not restricted to copper, as indicated inthe second embodiment. The pipe material may be made of other metalsthat have high heat conductivity, for example, copper alloy or aluminum.

A silicide ceramic other than silicon carbide such as silicon nitride(Si₃N₄) or sialon may be selected. In this case, it is preferred thatthe selected silicide ceramic be a dense body having a density of 2.7g/cm³ or greater.

The carbide ceramic may be, for example, boron carbide (B₄C), other thansilicon carbide. In this case, it is preferred that the selected carbideceramic is a dense body with a density of 2.7 g/cm³ or greater.

In the table 2 of the second embodiment, liquid other than water maycirculate in the pipe 16. Further, gas may circulate through the pipe16.

Third Embodiment

In a third embodiment, an improvement is made to further improve heatuniformity in the tables 2 of the first embodiment and its modifications(for the sake of brevity, these tables 2 are hereafter referred to astype A table 2). In the type A table 2, the grooves 13, which form partof the water passage 12, are formed in the upper side of the lower base11B. Thus, the lower side of the upper base 11A (the heat transmittingsurface with respect to the coolant water W that flows in the waterpassage 12) is flat.

In contrast, in the table 2 of the third embodiment, the groove 13 isformed in the lower side of the upper base 11A, as shown in FIGS. 11 and12. The grooves 13 are not formed in the upper side of the lower base11B.

It is preferred that the depth of the groove 13 is ⅓ to ½ of thethickness of the upper base 11A (in the third embodiment, 3 to 20millimeters).

When the groove 13 is not deep enough, the recesses formed in the lowerside of the upper base 11A are small and the heat transmitting area isinsufficient. Further, the flow passage cross-sectional area isinsufficient. This restricts the amount of the water coolant W thatflows in the water passage 12. Accordingly, the heat uniformity of thetable 2 is not sufficiently improved. In contrast, if the grooves 13 aretoo deep, the upper base 11A is partially thin. This would decrease therigidity of the upper base 11A. Accordingly, if the material of theupper base 11A is not optimally selected, the pressing force applied bythe plate 6 may damage the upper base 11A.

As schematically shown in FIG. 12, it is preferred that the grooves 13have a rectangular cross-section. More specifically, it is preferredthat the cross-section of each corner of the grooves 13 has an R of 0.3to 5. If the R is less than 0.3, stress concentration and machining mayform cracks and cause the table 2 to easily break. In contrast, if the Ris greater than 5, the flow passage cross-sectional area would beinsufficient, and the heat uniformity of the table 2 would not beimproved.

Further, it is preferred that the groove 13 be a ground groove or beformed by grinding the lower side of the upper base 11A with a grinder.If the grooves 13 are formed through grinding, the grooves 13 would havecorners having an R that is included in the optimal range and would havethe preferred cross-sectional form. In addition, grinding easily formsthe deep grooves 13 in a hard ceramic material such as a silicon carbidesinter.

The following is a referential example of the third embodiment.

Referential Example 3-1

In referential example 3-1, like referential example 1-1, the bases 11A,11B, which were formed of silicon carbide sinters, were molded, usingsilicon carbide powder as starting material, and calcinated.

Next, the groove 13 was formed in the lower side of the upper base 11Awith a grinder such that the groove 13 had a depth of 5 millimeters anda width of 10 millimeters and each corner of the groove 13 had an R ofone millimeter. The depth of the groove 13 was half of the thickness ofthe upper base 11A. The upper and lower bases 11A, 11B were thenintegrally brazed. After the brazing, the upper side of the upper base11A was polished to produce the table 2 having the polishing surface 2a.

The resulting table 2 of referential example 3-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers(silicon wafers) 5 of different dimensions were then polished with theapparatuses 1 while constantly circulating the coolant water W. Duringthe polishing, the temperature was measured at a number of points on thepolishing surface 2 a. The measurement indicated that the temperaturedifferences in the table 2 were extremely small (more specifically,within ±2 degrees Celsius from 40 degrees Celsius). In other words, theeffect of suppressing the heat variation was improved. Further, theobservation of the wafers 5 polished by the apparatuses 1 indicated thatthe wafers 5 were preferably formed, or were not damaged or bent at all,regardless of the dimensions of the wafers 5. In other words, it wasapparent that the semiconductor wafers 5 had an extremely high accuracyand high quality when using the table 2 of referential example 3-1.

Conclusion

Accordingly, the third embodiment has the following effects.

(1) The grooves 13, which form part of the water passage 12 in the table2, is formed in the lower side of the upper base 11A of the layeredceramic structure. That is, the lower side of the upper base 11Aincludes recesses to ensure sufficient heat transmitting area. Thus,compared to the first embodiment and its modifications, heat istransmitted to the water W more efficiently. This improves the heatuniformity of the table 2, thus making it relatively easy to control thetemperature by supplying fluid. Accordingly, the wafer 5 is machinedwith high accuracy such that the diameter of the wafer 5 is increasedand the quality of the wafer 5 is improved.

(2) In the table 2, the depth of the groove 13 is included in theaforementioned preferred range. This maintains the strength of the table2 and ensures sufficient heat transmitting area and sufficient flowpassage cross-sectional area. Thus, the durability of the table 2 andthe heat uniformity of the table 2 are improved.

(3) In the table 2, each corner of the rectangular cross section of thegroove 13 has an R included in the aforementioned preferred range. Thus,compared to a groove with a round cross-sectional shape of the samedepth as that of the groove 13, the groove 13 has a relatively largeflow passage cross-sectional area. This further improves the heatuniformity of the table 2.

The third embodiment may be modified as follows.

The bases 11A, 11B do not necessarily have to be joined together by thebrazing filler layer 14. For example, a bolt and a nut that fasten thebases 11A, 11B together, may replace the brazing filler layer 14. Thatis, the aforementioned structures of FIGS. 3 and 4 may be employed.

The grooves 13 do not necessarily have to be formed through grinding butmay be formed through blasting such as sand blasting. Further, thecross-section form of the groove 13 does not have to be generallyrectangular or cornered like in the third embodiment and may besubstantially V-shaped or semicircular.

Fourth Embodiment

The fourth embodiment employs the following structure to prevent thetype A table 2 from being flexed.

More specifically, the Young's modulus of the two bases 11A, 11B, whichare formed of ceramic, is 1.0 kg/cm²(×10⁶) or greater. It is preferredthat the Young's modulus be 1.0–10.0 kg/cm²(×10⁶) and is particularlypreferred that the Young's modulus be 1.0–5.0 kg/cm²(×10⁶). This isbecause when the Young's modulus is less than 1.0 kg/cm²(×10⁶), therigidity of the table 2 would be insufficient. Although a higher Young'smodulus is preferred, it would be difficult to procure material having aYoung's modulus that is greater than 10.0 kg/cm²(×10⁶) in an inexpensiveand stable manner.

The following is a referential example of the fourth embodiment.

Referential Example 4-1

In referential example 4-1, like referential example 3-1, the bases 11A,11B, which were formed from a silicon carbide sinter, were molded, usingsilicon carbide powder as a starting material, and calcinated. TheYoung's modulus of each base 11A, 11B was 3.5 kg/cm²(×10⁶). The upperbase 11A was then ground with a grinder, and the bases 11A, 11B werebrazed to each other. After the brazing, the upper side of the upperbase 11A was polished to complete the table 2 provided with thepolishing surface 2 a.

The resulting table 2 of referential example 4-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers(silicon wafers) 5 of different dimensions were then polished with theapparatuses 1 while constantly circulating the coolant water W. As aresult, flexing of the table 2 was not found, and the flatness of thepolishing surface 2 a was maintained.

The flatness of each wafer 5 polished by the apparatus 1 was alsomeasured. The measurement indicated that the flatness of each wafer 5was 2 micrometers or less in 600 millimeters Φ. Further, the flatness ofthe table 2 at 40 degrees Celsius was 5 micrometers or less. The wafers5 were not damaged. In other words, it was apparent that thesemiconductor wafers 5 had an extremely high accuracy, high quality, andlarge diameter when using the table 2 of referential example 4-1.

Conclusion

In the fourth embodiment, the bases 11A, 11B, or the components of thetable 2, are formed from a dense silicon carbide sinter that has a highYoung's modulus. The table 2 thus has the preferred rigidity. Thus,during usage, the table 2 is not flexed or deformed as a whole even if apressing force is applied to the polishing surface 2 a. This maintainsthe flatness of the polishing surface 2 a. Thus, the wafers 5 arepolished with high accuracy, and the flatness of the resulting wafers 5is increased. Accordingly, the table 2 enables the diameter of eachsemiconductor wafer 5 to be increased and improves the quality of thewafer 5.

The fourth embodiment may be modified as follows.

In the fourth embodiment, the table 2 has a double layered structure.However, the table 2 may have a triple layered structure. Alternatively,the table 2 may be a multiple layered structure that includes four ormore layers. Further, the water passage 12 may be eliminated such thatthe table 2 has a single layered structure (or a non-layered structure).

In the fourth embodiment, the groove 13 is formed in only the upper base11A. Alternatively, the groove 13 may be formed in only the lower base11B or both the upper and lower bases 11A, 11B.

In the fourth embodiment, the upper base 11A is formed of a densesilicon carbide sinter, and the lower base 11B is formed of a poroussilicon carbide sinter. However, the bases 11A, 11B are not restrictedto this combination. For example, both the upper and lower bases 11A,11B may be formed of dense or porous silicon carbide sinters.

A silicide ceramic other than silicon carbide, for example, siliconnitride or sialon may be selected. A carbide ceramic other than siliconcarbide, for example, boron carbide may be selected. Further, other thanthese types, oxide ceramic such as alumina or metal may be used. Ineither case, it is preferred Young's modulus be equal to or greater than1.0 kg/cm²(×10⁶)

Fifth Embodiment

The fifth embodiment includes the following structure to improve theheat uniformity and breakage strength of the A type table 2.

In the fifth embodiment, the brazing filler layer 14 arranged betweenthe bases 11A, 11B is formed by performing brazing with a brazing fillerthat contains silver as a main component (i.e., a brazing filler whichlargest component is silver). In this case, in addition to silver, it ispreferred that the brazing filler contain copper as another maincomponent (i.e., silver being the largest component and copper being thesecond largest component). Representative examples of the brazing fillerinclude silver brazing fillers such as BAg-1, BAg-1a, and BAg-2 (brazingfillers that contain silver and copper as main components and zinc andcadmium in small quantities), which are defined by JIS. Further, thebrazing filler may be BAg-3 (a brazing filler that contains silver andcopper as main components and zinc, cadmium, and nickel in smallquantities), BAg-4 (a brazing filler that contains silver and copper asmain components and zinc and nickel in small quantities), BAg-5 or BAg-6(a brazing filler that contains silver and copper as main components andzinc in a small quantity), or BAg-7 (a brazing filler that containssilver and copper as main components and zinc and tin in smallquantities). Further, it is preferred that a brazing filler with arelatively high melting temperature (for example, BAg-2, BAg-3, BAg-4,BAg-5, or BAg-6) be selected to enhance the heat resistance of thebrazing portion. In addition, a brazing filler that contains silver andcopper as main components but does not contain zinc or nickel or tin orcadmium, which are small quantity components in the aforementionedbrazing fillers, may be selected.

It is further preferred that each of the aforementioned brazing fillerscontains a small quantity of titanium (Ti) in addition to silver (Ag)and copper (Cu), which are the main components. Titanium has a largediffusion coefficient with respect to a sintered silicon carbide bodyand easily diffuses in the pores of the sintered body during thebrazing. The content of titanium in the brazing filler is preferably0.1–10 weight percent, and, more preferably, 1–5 weight percent.

It is preferred that the thickness of the brazing filler layer 14 formedfrom the aforementioned brazing fillers be approximately 10–50micrometers, and, more preferably, 20–40 micrometers, from the viewpointof joining strength and cost.

The fifth embodiment also has the following improvement to prevent thetable 2 from being flexed by thermal stress and to improve the flatnessof the wafers 5.

More specifically, the bases 11A, 11B of the fifth embodiment havesubstantially equal thermal expansion coefficients. That is, thedifference of the thermal expansion coefficient between the bases 11A,11B is preferably 1.0×10⁻⁶/degree Celsius or smaller, more preferably0.5×10⁻⁶/degree Celsius or smaller, and, further preferably,0.2×10⁻⁶/degree Celsius or smaller. As the difference becomes smaller,the thermal stress that would otherwise cause flexing or cracking isfurther prevented from being generated.

The thermal expansion coefficient of each base 11A, 11B at 0–400 degreesCelsius is preferably 8.0×10⁻⁶/degree Celsius or smaller, morepreferably 6.5×10⁻⁶/degree Celsius or smaller, and, most preferably,5.0×10⁻⁶/degree Celsius or smaller. This maximally suppresses thedifference between the thermal expansion coefficient of silicon, or3.5×10⁻⁶/degree Celsius, and the thermal expansion coefficient of thetable 2. Further, it is preferred that the thermal expansion coefficientof each base 11A, 11B at 0–400 degrees Celsius be equal to or largerthan 2.0×10⁻⁶/degree Celsius.

The fifth embodiment further has the following improvement to improvethe heat uniformity of the table 2.

More specifically, it is preferred that the heat conductivity TC1 of theupper base 11A, which is formed from ceramic, be equal to or larger thanthe heat conductivity TC2 of the lower base 11B, which is also formedfrom ceramic, thus satisfying the following condition of TC1≧TC2. In thefifth embodiment, a dense body with strongly bonded crystal particlesand an extremely small number of pores is selected as the material ofthe upper base 11A. In contrast, a porous body with a large number ofpores is selected as the material of the lower base 11B. Further, theupper base 11A is thinner than the lower base 11B. The anti-heatresistance of the upper base 11A is thus lower than that of the lowerbase 11B. More specifically, it is preferred that the thickness of theupper base 11A be 3–20 millimeters and the thickness of the lower base11B be 10–50 millimeters.

If the upper base 11A is formed from a silicon carbide sinter, it ispreferred that the heat conductivity of the upper base 11A be 40 W/m·Kor higher, and, more preferred that the heat conductivity be 80–200W/m·K. If the heat conductivity is too low, temperature differences tendto be produced. This interferes with increasing the diameter andimproving the quality of the semiconductor wafer 5. In contrast,although it is preferred that the heat conductivity be greater, materialhaving heat conductivity that is greater than 200 W/m·K is difficult toprocure inexpensively and stably. If the lower base 11B is formed from asintered silicon carbide body, the heat conductivity of the sinteredbody is preferably 5 W/m·K or higher, and, more preferably, 10–40 W/m·K.This prevents heat from being released from an area lower than the waterpassage 12, or a cooling portion, thus making it easy to control thetemperature of the polishing surface 2 a.

The following are referential examples of the fifth embodiment.

Referential Example 5-1

To form the upper base 11A, “beta random (trade name)”, product ofIBIDEN KABUSHIKI KAISHA, was used as silicon carbide powder thatcontained 94.6 weight percent of β type crystals. The average crystalparticle diameter of the powder was 1.3 micrometers. The powdercontained 1.5 weight percent of boron and 3.6 weight percent of freecarbon.

First, 5 weight parts of polyvinyl alcohol and 300 weight parts of waterwere added to 100 weight parts of the silicon carbide powder. Themixture was then stirred in a ball mill for five hours to obtain auniform mixture. The mixture was dried for a predetermined time toremove a certain amount of moisture from the mixture. The dry mixturewas then sampled in an appropriate amount. The sample was granulated.Next, the granules of the dry mixture were molding with metal press diesat a pressure of 50 kg/cm². The density of the resulting molded body was1.2 g/cm³.

Subsequently, the lower side of the body that forms the upper base 11Awas ground to form the groove 13 having a depth of 5 millimeters and awidth of 10 millimeters.

Next, the molded product was placed in a graphite crucible sealed fromambient air. The body was then calcinated using a Tammann typecalcinating furnace. The calcination was performed in an argon gasatmosphere of one atmospheric pressure. During the calcination, thetemperature was increased at a rate of 10 degrees Celsius per minute toa maximum temperature of 2300 degrees Celsius. The maximum temperaturewas maintained for two hours. The observation of the resulting upperbase 11A revealed an extremely dense, three-dimensional networkstructure in which plate crystals were entangled in multiple directions.Further, the density of the upper base 11A was 3.1 g/cm³. The heatconductivity (TC1) of the upper base 11A was 150 W/m·K. The upper base11A contained 0.4 weight percent of boron and 1.8 weight percent of freecarbon. The diameter of the upper base 11A was 600 millimeters, and thethickness of the upper base 11A was 5 millimeters.

As for the lower base 11B, a commercially available porous siliconcarbide sinter (more specifically, “SCP-5 (trade name)”, product ofIBIDEN KABUSHIKI KAISHA) was used. The density of the sintered body wasapproximately 1.9 g/cm³, and the heat conductivity (TC2) of the sinteredbody was 30 W/m·K. Further, the porosity of the sintered body was40–45%. The diameter of the resulting lower base 11B was 600millimeters, and the thickness of the base 11B was 25 millimeters. Thethermal expansion coefficient of the upper base 11A at 0–400 degreesCelsius was 4.5×10⁻⁶/degrees Celsius, and the thermal expansioncoefficient of the lower base 11B at 0–400 degrees Celsius was4.4×10⁻⁶/degrees Celsius. The difference of the thermal coefficientbetween the upper and lower bases 11A, 11B was 0.1×10⁻⁶/degrees Celsius.

The two bases 11A, 11B were then integrally brazed to each other. Afoil-like brazing filler having a thickness of 50 micrometers was used.The brazing filler contained 63 weight percent of silver, 35 weightpercent of copper, and 2 weight percent of titanium. In other words, thebrazing filler contained silver and copper as main components andtitanium in a small quantity. The heating temperature for brazing was850 degrees Celsius, which was the melting temperature of the brazingfiller. The thickness of the brazing filler layer was 20 micrometers.

After the brazing, the upper side of the upper base 11A was polished toform the table 2 provided with the polishing surface 2 a.

The resulting table 2 of referential example 5-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers(silicon wafers) 5 having different dimensions were then polished by theapparatuses 1 at a high temperature of several hundreds of degreesCelsius, while constantly circulating the coolant water W. As a result,no flexing of the table 2 was found. Further, no cracks were found inthe brazing filler layer 14, and the bonding strength was maintained inthe joining interface between the bases 11A, 11B. Also, a breakage testwas conducted on the table 2 using a conventional method complying withJIS R 1624 to measure the flexural strength of the interface. The valuewas approximately 30 kgf/mm². Further, no leaks of coolant water W fromthe joining interface were noted.

The observation of the wafers 5 polished by the apparatuses 1 indicatedthat the wafers 5 were not damaged, regardless of the dimensions of thewafers 5. Further, no significant bending was noted in the wafers 5.More specifically, the flatness of each wafer 5 was 2 micrometers orless in 600 millimeters Φ. Further, the flatness of the table 2 at 40degrees Celsius was 5 micrometers or less.

In other words, it was apparent that the semiconductor wafers 5 producedusing the table 2 of referential example 5-1 had an extremely highaccuracy and high quality.

Referential Example 5-2

Subsequently, the table 2 like that of referential example 5-1 wasfabricated using a general silver brazing filler that contained notitanium (BAg-6; containing 50 weight percent of silver, 34 weightpercent of copper, and 16 weight percent of zinc). A breakage test wasconducted with the resulting table 2 of referential example 5-2, and thebending strength of the joining interface was measured through themethod complying with JIS R 1624. The measured value was 10 kgf/mm²,which is lower that that of referential example 4-1. In other words,compared to referential example 5-1, the bonding strength of the joininginterface of the table 2 of referential example 5-2 was lower. Further,although no cracks were currently found, it was assumed that the table 2would be damaged due to cracking if the table 2 was continuously usedfor a long time.

Conclusion

Accordingly, the fifth embodiment has the following effects.

(1) The brazing filler layer 14 arranged between the bases 11A, 11Bcontains a predetermined amount of titanium that has an increaseddiffusion coefficient with respect to the sintered silicon carbide body.Thus, during the brazing, titanium diffuses in the pores of the sinteredbody, thus ensuring a sufficient bonding strength in the joininginterface between the bases 11A, 11B. Accordingly, regardless oflong-term use, damages of the joining interface caused by cracking areprevented. The strength of the table 2 is thus improved.

Further, the brazing filler is a non-organic joining material. Thebrazing filler does not deteriorate or change quality even when exposedto a high temperature of several hundreds of degrees Celsius. Thismaintains the bonding strength of the joining interface. Accordingly,the table 2, formed by such brazing filler, has improved anti-heatresistance compared to when using an organic joining material.

(2) The brazing filler of the table 2 of the fifth embodiment has a highheat conductivity compared to an organic joining material such as anadhesive agent. This reduces the anti-heat resistance in the joiningsurface. The temperature differences in the table 2 are thus decreased.Accordingly, compared to when the table 2 is mounted on a cooling jacketto indirectly cool the table 2, heat is efficiently released from thetable 2. This further decreases the temperature differences in the table2. As a result, the heat uniformity of the table 2 is improved. Further,this enables the diameter of each semiconductor wafer 5 to be increasedand improves the quality of the wafer 5.

(3) In the table 2 of the fifth embodiment, the bases 11A, 11B arebrazed together by the brazing filler layer 14 that contains silver andcopper as main components. The brazing filler layer 14 is formed with arelatively inexpensive brazing filler. This reduces the cost of thetable 2. Further, the titanium content of the brazing filler layer 14 isselected to be in a preferred range of 0.1–10 weight percent. Thisfurther improves the bonding strength between the bases 11A, 11B.

(4) The foil-like brazing filler used in the table 2 of the fifthembodiment is easily handled. This facilitates the brazing, thus makingit easy to fabricate the table 2. Further, the foil-like brazing filleris arranged in the joining interface so that it has a uniform thickness.This increases the joining strength of the joining interface and sealsthe joining interface. Accordingly, when the coolant water W flows inthe water passage 12, the water W does not leak from the water passage12. This maintains the cooling capability.

(5) The table 2 is formed by the silicon carbide bases 11A, 11B thathave substantially equal thermal expansion coefficients. Thus, even ifthe table 2 is exposed to a high temperature, generation of thermalstress, which otherwise bends the table 2 as a whole, is suppressed.This prevents the table 2 from being flexed and increases the flatnessof each wafer 5. As a result, the table 2 enables the diameter of eachwafer 5 to be increased and improves the quality of the wafer 5.

(6) The heat conductivity TC1 of the upper base 11A is higher than theheat conductivity TC2 of the lower base 11B. Thus, heat is rapidlytransmitted from the polishing surface 2 a to the interior of the table2 through the upper base 11A, which has the relatively high heatconductivity. The heat is thus transmitted to the coolant water W in thewater passage 12. Accordingly, compared to the prior art in which thetable 2 is mounted on the cooling jacket to indirectly cool the table 2,heat is efficiently released from the table 2. This reduces thetemperature differences in the table 2. As described above, the heatuniformity of the table 2 is improved. The temperature of the table 2 iscontrolled relatively easily and accurately through the fluid supply.This contributes to increasing the diameter of each wafer 5 andimproving the quality of the wafer 5.

The fifth embodiment may be modified as follows.

The brazing filler that joins the bases 11A, 11B together is notrestricted to the brazing fillers containing silver as a main componentlike in the fifth embodiment. Other hard brazing fillers, such as goldbrazing fillers, may be used as the brazing filler. However, in terms ofcost, it is preferable to select a brazing filler that contains silveras a main component.

In the fifth embodiment, the upper base 11A is formed of a dense siliconcarbide sinter, and the lower base 11B is formed of a porous siliconcarbide sinter. However, the materials of the bases 11A, 11B are notrestricted to this combination. Instead, for example, both the bases11A, 11B may be formed of dense or porous silicon carbide sinters.

As shown in FIG. 5, the table 2 may have a triple layered structure thatincludes the bases 11A, 11B, and 11C. In this case, the heatconductivity TC1 of the base 11A is equal to or greater than the heatconductivity TC2 of the base 11B. Further, the heat conductivity TC2 ofthe base 11B is equal to or greater than the heat conductivity TC3 ofthe base 11C. That is, it is preferred that the following condition besatisfied: TC1≧TC2≧TC3. In addition, if the table 2 has four or morelayers, a similar condition must be met.

Organic joining materials, such as epoxy resin adhesive agents, mayreplace the non-organic joining materials, such as the brazing fillers.

Sixth Embodiment

A sixth embodiment has the following improvement for further increasingthe joining interface strength of the A type table 2 and the tables 2 ofthe second embodiment and its modifications (for the sake of brevity,these tables 2 are hereafter referred to as a B type table 2) when anorganic joining material is employed.

As shown in FIG. 13, in the sixth embodiment, the bases 11A, 11B arejoined together by the organic adhesive agent layer 14. Particularly, inthis embodiment, the organic adhesive agent layer 14 is formed from anepoxy resin type adhesive agent. More specifically, the adhesive agentof the adhesive agent layer 14 is formed from epoxy resin, transformedpolyamine, and silicon oxide (SiO₂) that are mixed in accordance with apredetermined ratio. This adhesive agent has a preferable property inthat it resists expansion when exposed to water. It is preferred thatthe adhesive agent has a thermosetting property. Also, the thickness ofthe adhesive agent layer 14 is preferred to be approximately 10–50micrometers, and, is more preferred to be approximately 20–40micrometers.

If the adhesive agent layer 14 is too thin, a sufficient adhesionstrength cannot be obtained and the bases 11A, 11B easily separate fromeach other. Further, the modulus of elasticity of the organic adhesiveagent is smaller than that of ceramic. Accordingly, if the thickness ofthe adhesive agent layer 14 is excessively large, cracking easily occursin the adhesive agent layer 14 when stress is applied. In addition, theheat conductivity of the organic adhesive agent is smaller than that ofceramic. Thus, if the adhesive agent layer 14 is too thick, the heatresistance of the adhesive agent layer 14 increases and hinders theimprovement of the heat uniformity of the table 2.

It is preferred that a processed modified layer L1 defined in a surfacelayer of the lower surface of the upper base 11A or the upper surface ofthe lower base 11B, which function as adhered surfaces, have a thicknessof 30 micrometers or less. It is further preferred that the thickness be10 micrometers or less, and particularly preferred that the thickness beone micrometer or less (see FIG. 13B). A surface exposing processperformed after the calcinating step produces the processed modifiedlayer L1, which has a thickness of approximately several tens ofmicrometers, in the surface layer of the bases 11A, 11B.

If the organic adhesive agent is used and the thickness t1 of each zoneL1 is greater than 30 micrometers, the processed modified layers L1 arelikely to fall off and the adhering strength becomes insufficient. Ifpossible, as shown in FIG. 13C, it is desirable that the processedmodified layers L1 be completely removed. In this case, a grain boundaryof crystal particles G1 is exposed from the surface layer of each basesuch that the adhesive agent layer 14 is embedded in the grain boundary,thus presumably ensuring an extremely high anchoring effect (see FIG.14).

It is preferred that the surface roughness Ra of the lower side of theupper base 11A and the surface roughness Ra of the upper side of thelower base 11B be 0.01–2 micrometers, and is particularly preferred tobe 0.1–1.0 micrometers. If the organic adhesive agent is used and Ra isincluded in the aforementioned ranges, a preferable anchoring effect isobtained in the surfaces of ceramic.

When Ra is less than 0.01 micrometers, the adhered surfaces of the bases11A, 11B are smoothened such that there are no pits and lands. Theorganic adhesive agent thus cannot be embedded in the sintered ceramicbodies. In this case, the preferable anchoring effect cannot beobtained. Further, to make Ra less than 0.01 micrometers, a specialprocess must be performed. This increases costs and lowers productivity.In addition, if Ra is greater than 2 micrometers, the preferableanchoring effect cannot be obtained.

A procedure for fabricating the table 2 will hereafter be describedbriefly.

First, like the first embodiment, disk-like molded products are moldedwith metal molds using silicon carbide powder as a starting material.The grooves 13 are ground in the lower side of a molded body that formsthe upper base 11A. The body is then calcinated at 1800–2400 degreesCelsius. The bases 11A, 11B formed of sintered silicon carbide bodiesare thus obtained.

After the calcination, a surface exposing process is performed to reduce(or completely remove) the processed modified layers L1 in the lowerside of the upper base 11A and the upper side of the lower base 11B.Examples of a layer thinning process or a removal processes include amechanical process such as a surface grinding using a grinder. Achemical process may be performed instead of the mechanical process. Inthe sixth embodiment, the chemical process is performed by etching withan acid etchant that melts silicon carbide. More specifically, theetching uses an etchant formed by adding a predetermined amount of weakacid to hydrofluoric-nitric acid. The weak acid includes organic acidsuch as acetic acid. The weight ratio of the component ofhydrofluoric-nitric-acetic acid, or hydrofluoric acid:nitric acid:aceticacid, is preferably 1:2:1. As a result of the processing, the surfaceroughness Ra of the lower side of the upper base 11A and the upper sideof the lower base 11B is adjusted and included in a range of 0.01–2micrometers.

Subsequently, organic adhesive agent is applied to the upper side of thelower base 11B. The bases 11A, 11B are then superimposed. In this state,the bases 11A, 11B are heated to the hardening temperature of resin,thus adhering the bases 11A, 11B together. Finally, the upper side ofthe upper base 11A is polished to complete the table 2.

The followings are referential examples of the sixth embodiment.

Referential Example 6-1

In referential example 6-1, “beta random (trade name)”, product ofIBIDEN KABUSHIKI KAISHA, was used as silicon carbide powder thatcontained 94.6 weight percent of β type crystals.

First, 5 weight parts of polyvinyl alcohol and 300 weight parts of waterwere added to 100 weight parts of the silicon carbide powder. Themixture was then stirred in a ball mill for 5 hours to obtain a uniformmixture. The mixture was dried for a predetermined time to remove acertain amount of moisture from the mixture. An appropriate amount ofthe dry mixture was then sampled and granulated. Next, the granules ofthe dry mixture were molded with metal press dies at a pressure of 50kg/cm².

The substantially entire lower side of a molded body that forms theupper base 11A was then ground to form the grooves 13 having a depth of5 millimeters and a width of 10 millimeters.

Subsequently, the molded body was placed in a graphite crucible sealedfrom ambient air. The body was then calcinated using a Tammann typecalcinating furnace. The calcination was performed in an argon gasatmosphere of one atmospheric pressure. During the calcination, thetemperature was increased at a rate of 10 degrees Celsius per minute toa maximum temperature of 2300 degrees Celsius. The heat was maintainedfor two hours. The density of each resulting base 11A, 11B was 3.1g/cm³. The heat conductivity of each base 11A, 11B was 150 W/m·K.

Next, a surface exposing process was performed using a conventionalmethod. Afterwards, surface grinding was performed as the layer thinningprocess. In this manner, the thickness t1 of the processed modifiedlayer L1 of the lower side of the upper base 11A and that of the upperside of the lower base 11B were adjusted to be approximately onemicrometer. Ra was included in the range of 0.01–2 micrometers.Subsequently, the bases 11A, 11B were integrally adhered to each otherby an epoxy resin type adhesive agent (“EP-169”, trade name, product ofCEMEDINE). The thickness of the organic adhesive agent layer 14 wasapproximately 20 micrometers. The hardening temperature was 160 degreesCelsius, the hardening time was 90 minutes, and the load applied foradhesion was 10 g/cm².

Further, the upper side of the upper base 11A was polished to completethe table 2.

The resulting table 2 of referential example 6-1 was installed in theaforementioned various types of apparatuses 1. The semiconductor wafers5 of different dimensions were then polished with the apparatuses 1,while constantly circulating the coolant water W. As a result, therewere no thermal deformations in the table 2. Further, no cracks werefound in the organic agent layer 14, and a high strength was maintainedin the joining interface between the bases 11A, 11B. Also, a breakagetest was conducted on the table 2 using a conventional method complyingwith JIS R 1624 to measure the bending strength of the interface. Theresult was approximately 10 kgf/mm². Further, there was no leakage ofthe coolant water W from the joining interface.

The observation of the semiconductor wafers 5 polished by theapparatuses 1 indicated that the wafers 5 were not damaged, regardlessof the dimensions of the wafers 5. Further, no significant bending wasnoted in the wafers 5. In other words, it was apparent that thesemiconductor wafers 5 produced by the table 2 of referential example6-1 had an extremely high accuracy and high quality.

Referential Example 6-2

In referential example 6-2, a type silicon carbide powder (morespecifically, “OY15 (trade name)”, product of YAKUSHIMA DENKO KABUSHIKIKAISHA) was employed, instead of the β type. The density of eachresulting base 11A, 11B was 3.1 g/cm³. The heat conductivity of eachbase 11A, 11B was 125 W/m·K. Each base 11A, 11B contained 0.4 weightpercent of boron and 1.8 weight percent of free carbon. Further, thesurface exposing process and the surface grinding were performed toadjust the thickness t1 of the processed modified layer L1 of eachadhering surface to approximately 5 micrometers. Ra was included in therange of 0.01–2 micrometers.

After producing the table 2 through the same procedure as referentialexample 6-1, the table 2 was installed in the various types ofapparatuses 1 to polish the semiconductor wafers 5 of differentdimensions. Accordingly, substantially the same advantageous results asthose of referential example 6-1 were obtained. Further, no cracks werefound in the organic adhesive agent layer 14, and the strength of theadhering interface between the bases 11A, 11B was high. The measurementof the bending strength under JIS R 1624 indicated that the averagevalue of the bending strength was approximately 8 kgf/mm². In otherwords, referential example 6-2 with the starting material of α typesilicon carbide powder was slightly improved in the adhering strength,as compared to referential example 6-1 with the starting material of βtype silicon carbide powder.

Referential Examples 6-3, 6-4, 6-5

In these referential examples, the table 2 was produced basicallythrough the same procedure as referential example 6-1. Further, inreferential example 6-3, the thickness t1 of each machining modifiedzone L1 after the surface grinding was adjusted to approximately 10micrometers. In referential example 6-44, the thickness t1 was adjustedto approximately 20 micrometers. In referential example 6-5, thethickness t1 was adjusted to be approximately zero micrometers (theprocessed modified layer L1 was completely removed). In both referentialexamples, Ra was included in the range of 0.01–2 micrometers.

The resulting table 2 was installed in the aforementioned various typesof polishing apparatuses 1. The semiconductor wafers 5 of differentdimensions were then polished. As a result, substantially the sameadvantageous effects as those of referential example 6-1 were obtained.Further, no cracks were noted in the organic adhesive agent layer 14,and the strength of the adhering interface between the bases 11A, 11Bwas high. The measurement of the bending strength under JIS R 1624indicated that the averages of referential examples 6-3, 6-4, and 6-5were approximately 7 kgf/mm², approximately 6 kgf/mm², and approximately12 kgf/mm², respectively.

Referential Examples 6-6, 6-7

In referential example 6-6, the surface exposing process was performedafter the calcination. However, the surface grinding, which wouldotherwise be performed after the surface exposing process, was notperformed. The bases 11A, 11B were adhered together with the epoxy resintype adhesive agent “EP-160”.

In referential example 6-7, the surface exposing process was performedafter the calcination. However, the surface grinding, which wouldotherwise be performed after the surface forming machining, was notperformed. The bases 11A, 11B were adhered together with an epoxy resintype adhesive agent (“CEMEDINE 100”, trade name), which differs from thetype used in the aforementioned referential examples. The thickness ofthe processed modified layer L1 of each adhering surface wasapproximately 35 micrometers and was much thicker than those of theaforementioned referential examples. Further, the value Ra of theadhering surface was 3.0 micrometers.

The measurement of the bending strength under JIS R 1624 was performedwith the resulting table 2. The result indicated that the average valuesof referential examples 6-6 and 6-7 were approximately 4 kgf/mm² andapproximately 1 kgf/mm², respectively. In other words, the adheringstrength was not high like in referential examples 6-1, 6-2, 6-3, 6-4,and 6-5.

Conclusion

Accordingly, the sixth embodiment has the following effects.

(1) In the bases 11A, 11B of the table 2 of the sixth embodiment, thethickness t1 of the processed modified layer L1 of each adhering surfaceis 30 micrometers or less and Ra of each adhering surface is included inthe range of 0.01 millimeters to 2 micrometers. Accordingly, even thoughthe organic adhesive agent is used, the organic adhesive agent layer 14has a sufficient strength. This suppresses cracking and peeling of theadhering interface. The table 2 is resists breakage and is practical.Further, the seal performance of the adhering interface is maintained toprevent the coolant water W in the water passage 12 from leaking fromthe adhering interface.

(2) In the sixth embodiment, the thickness of the organic adhesive agentlayer 14 is selected from a range of 10–50 micrometers. This improvesthe heat uniformity of the table 2 and enables the adhering interface tohave sufficient strength.

The sixth embodiment may be modified as follows.

As shown in FIG. 15, the copper pipe 16 may be located in the grooves13. Coolant water may be circulated through the copper pipe 16.

As shown in FIG. 16, the powder (for example, the copper powder) 17,which is formed from a substance having high heat conductivity, may bemixed as a filler in the organic adhesive agent 14 at least around thecopper pipe 16.

The present invention is not restricted to the first to sixthembodiments but may be modified within the scope of the appended claims.

1. A table having a polishing surface for polishing a semiconductorwafer held by a wafer holding plate of a wafer polishing apparatus,wherein the table includes a plurality of superimposed bases, each basebeing formed from calcinated silicide ceramic or carbide ceramic,wherein the density of each base is at least 2.7 g/cm³, and wherein atleast one of the bases has a fluid passage formed in its superimpositioninterface.
 2. A table having a polishing surface for polishing asemiconductor wafer held by a wafer holding plate of a wafer polishingapparatus, wherein the table includes a plurality of superimposed bases,each base being formed from a silicon carbide sinter, wherein thedensity of each base is at least 2.7 g/cm3, and wherein at least one ofthe bases has a fluid passage formed in its superimposition interface.3. The table according to claim 1 or 2, wherein at least one baseincludes a groove formed in the superimposition interface and formingpart of the fluid passage.
 4. The table according to claim 1 or 2,further comprising a plurality of adhering layers for joining the bases.5. The table according to claim 1 or 2, wherein at least one of thebases is arranged on an uppermost level of the superimposed bases andincludes the polishing surface and a groove formed in a surface locatedon an opposite side of the polishing surface to form part of the fluidpassage.
 6. The table according to claim 5, wherein the groove has adepth that is ⅓ to ½ the thickness of the base.
 7. The table accordingto claim 6, wherein the groove has a corner, the R of which is 0.3 to 5.8. The table according to claim 7, wherein the groove is formed throughmachining before the base is formed through calcination.
 9. The tableaccording to claim 1 or 2, further comprising a brazing filler layer forjoining the bases that contains titanium.
 10. The table according toclaim 9, wherein the brazing filler layer contains silver as a maincomponent.
 11. The table according to claim 10, wherein the content oftitanium in the brazing filler layer is 0.1 weight percent to 10 weightpercent.
 12. The table according to claim 1 or 2, wherein the bases havesubstantially the same thermal expansion coefficients.
 13. The tableaccording to claim 12, wherein the thermal expansion coefficient of eachof the bases is 8.0×10⁻⁶/degrees Celsius or less.
 14. The tableaccording to claim 12, wherein the thermal expansion coefficient of eachof the bases is 5.0×10⁻⁶/degrees Celsius or less.
 15. The tableaccording to claim 14, wherein the difference of the thermal expansioncoefficient between the base is 1.0×10⁻⁶/degrees Celsius or less. 16.The table according to claim 1 or 2, wherein the heat conductivity of afirst base located near the polishing surface is greater than or equalto that of a second base, which is in a level lower than the first base.17. The table according to claim 16, wherein the first base is thinnerthan the second base.
 18. The table according to claim 16, wherein thefirst base is a dense silicon carbide sinter, and the second base is aporous silicon carbide sinter.
 19. The table according to claim 1 or 2,further comprising a plurality of organic adhesive agent layers forjoining the bases, wherein a processed modified layer having a thicknessof 30 micrometers or less is formed in a joining surface of the organicadhesive agent layer in each of the bases.
 20. The table according toclaim 19, wherein each of the organic adhesive agent layers has athickness of 10 micrometers to 50 micrometers.
 21. The table accordingto claim 1 or 2, further comprising a plurality of organic adhesiveagent layers for joining the bases, wherein the surface roughness (Ra)of a joining surface of the organic adhesive agent layer in each of thebases is 0.01 micrometers to 2 micrometers.
 22. The table according toclaim 21, wherein each of the organic adhesive agent layers has athickness of 10 micrometers to 50 micrometers.
 23. The table accordingto claim 1, wherein the heat conductivity of each base is at least 30W/mK or greater.
 24. The table according to claim 23, wherein at leastone base includes a groove formed in the superimposition interface andforming part of the fluid passage, and the table further includes a pipelocated in the groove and formed from a high heat conductivity material.25. The table according to claim 24, wherein the groove has a roundcross-sectional form.
 26. The table according to claim 24, wherein theadhering layers at least around the pipe contain powder formed of a highheat conductivity substance.
 27. The table according to claim 26,wherein the powder is copper powder, and the pipe is a curved copperpipe.
 28. The table according to claim 1, wherein the Young's modulus ofeach of the bases is at least 1.0 kg/cm²(×10⁶) or greater.
 29. The tableaccording to claim 2, wherein the Young's modulus of each base is 1.0 to5.0 kg/cm²(×10⁶).
 30. The table according to claim 1, wherein the fluidpassage is a water passage.
 31. The table according to claim 1, whereinthe at least one of the bases has a through hole communicated with thefluid passage.
 32. The table according to claim 1, wherein the ceramiccontains β type silicon carbide powder.
 33. The table according to claim1, wherein the plurality of superimposed bases are formed throughcalcination at at least 1800 degree.
 34. The table according to claim 2,wherein the fluid passage is a water passage.
 35. The table according toclaim 2, wherein the at least one of the bases has a through holecommunicated with the fluid passage.
 36. The table according to claim 2,wherein the ceramic contains β type silicon carbide powder.
 37. Thetable according to claim 2, wherein the plurality of superimposed basesare formed through calcination of at least 1800 degree.